Most of our knowledge about genetic influences in substance abuse come from adoption and twin studies of alcoholism. Only a few abstracts and journal articles have addressed the issue of genetic influences in human drug abuse. Yet, this information is important for our understanding of the etiology and prevention of drug problems. We are using DIS interview information as well as questionnaire data from the Minnesota Twin Registry to estimate extent of genetic involvement in drug abuse (marijuana, amphetamine, barbiturates, tranquilizers, cocaine, heroine and other opiates, psychedelics, and other drugs). Data are being analyzed to determine heritability of drug use (i.e., use over 5 times in lifetime), problem use, and DSM III clinical diagnosis. The statistical tool of path analysis will be used to estimate the contributions of genetic and environmental influences to the variation in the above described measures.